After three years, or more, service, the thin, elongated fuel pins, or rods, of a nuclear reactor often have warp, or distortions, along their lengths. It is now contemplated to store these fuel rods of the assemblies, individually. Once the fuel rods are removed from their assemblies, their arrangement and support in the poison storage boxes has distinctive problems.
Concern for the storage provisions for spent nuclear fuel assemblies is found in at least U.S. Pat. No. 4,177,385, Bevilacqua, and U.S. patent application Ser. No. 142,585 filed Apr. 21, 1980. These prior disclosures explore the problems, and their solutions, of providing box inserts in storage racks for complete fuel assemblies. The boxes may be poisoned with various arrangements and provided with flux traps within their storage rack. The fundamental objective is to store the spent fuel for a significant decay time, awaiting ultimate disposal. With all the concern for the construction of the box inserts, their vertical suspension in the storage rack, and the provision of poison arrangements, there has been no prior contemplation of reducing the size of the storage, or increasing its capacity, by breaking down the fuel rod assembly and transferring the individual rods into the box in a more compact arrangement than in the fuel assembly.
There is need for a base plate construction at the lower end of the storage box insert which will not only support the fuel rods, vertically, but which will inherently organize the rods laterally into a compact body. This base plate construction not only provides support and organization of the fuel rods, but allows circulation of cooling water through the length of the storage box insert. Further, the construction of the base plate must provide for its remote insertion into existing forms of storage box inserts and permanent installations of the bases when boxes are initially assembled.